Don inspects a crossword puzzle with hidden clues that could have jeopardized D-Day; one of the most important maps in world history, which was nearly lost forever; and an odd-looking traffic signal that became a cultural symbol for communist East Germany.

Don examines a sleek American race car that took on a top Italian automaker; a pulp-fiction science magazine that threatened to expose an explosive World War II secret; and a set of teeth that was key in the biggest public health experiments of the 20th century.